The sixpence (also spelled six pence as two words), abbreviated as 6d (from 6 denarii, the Latin word for a small silver denomination) had been a regular circulating coin of the pre-decimal Pound Sterling since the reign of King Edward VI in England (1547 - 1553); it was equal to 6/240 of a pound. The coin went through many changes until the 20th century, when it was first debased from sterling silver to 0.500 silver, then changed to copper-nickel.
After decimalisation in 1971, the pre-decimal sixpence denomination had no equivalent in the new decimal system and was demonetised in 1980. Throughout its history as a circulating coin, it had traditionally been used also as a wedding gift, with a popular Old English rhyme going, "Something Olde, Something New, Something Borrowed, Something Blue, A Sixpence in your Shoe" - which names the four good-luck objects, plus a sixpence to bring prosperity, that a bride should include somewhere in her wedding outfit or carry with her on her wedding day. The bride’s father would give her a silver sixpence to place in her left shoe to bring the happy couple prosperity in their life together.
Another age-old British Christmas tradition is for families to stir a Christmas silver sixpence coin into their Christmas pudding for good fortune. Stir-up-Sunday, the last Sunday before Advent, is the traditional day to make the Christmas pudding. Traditionally, a silver sixpence was stirred into the mix, to bring the finder wealth and good luck in the year to come. In the past it was usual for every member of the household to give the pudding a stir and make a wish. Some families have used the same Christmas sixpence for as long as they can remember.
In 2016, the the Royal Mint revived that tradition when it started issuing sixpence coins again, with a new reverse design by John Bergdahl. These are denominated as 6 new (decimal) pence and have the composition of the pre-1920 sterling silver coins. The Royal Mint sells them in gift packaging suitable for the occasion (wedding or Christmas); although legal tender, these coins are not meant for circulation.